(i) Field Covered by the Invention
The present invention relates to a process for the operation of a system comprising at least one absorption heat pump, in which a working medium or fluid is generated or expelled, by the input of heat energy at a relatively high temperature, from an absorption material, the generated working medium is condensed, the condensed working medium undergoes expansion, the expanded, condensed working medium is evaporated by the input of heat energy at a relatively low temperature, and the evaporated working medium is lastly absorbed again in the absorption material. Furthermore, the invention relates to forms of plant for effecting such a process.
(ii) The Prior Art
For making the best economic use of fossil and nuclear energy supplies on hand, heat pumps have of late come to play an increasingly important part for heating purposes, in addition to their use in refrigeration and cooling systems, which have been in existence for a much longer time. One shortcoming in this connection, which has so far not been completely taken care of, is with respect to supplying a heat pump with input energy. Compressor heat pumps, powered by an electric motor, have the shortcoming of needing their own, further power from the public electricity line and such further power may well be, in fact, needed at the same time as the peak load on the public electricity line. This is true not only for heating, but furthermore for cooling (that is to say generally "temperature control") of rooms. While it is true that this shortcoming may be taken care of by the heat pump only being run at off-peak times, more specially overnight, and by the heat or cold being stored in a heat or cold storing unit, from which it may then be taken as needed, the heat coming from a heat pump is generally at low temperatures so that low-temperature heat storing units of great size would be needed for storing the necessary amount of heat. Much the same would furthermore be true for the storing of cold.
Absorption heat pumps may be supplied with input power or energy by oil or gas burners so that some of the shortcomings noted for electric motor-powered compressor heat pumps are taken care of. Absorption heat pumps, supplied with input power by a gas or oil burner, have, however, their own special shortcomings: Economic use of the primary energy makes it necessary for the cold and/or heat output of the heat pump to be kept in step with the heat need at the time in question, that is to say the plant's output rate has to be controllable. However, stepless control of oil burners has turned out to be difficult. On-off automatic control has, on the one hand, not given anything like the same efficiency as continuous control and, furthermore, at times when the heat need is generally low, in which the on-times of the burner are generally short and separated by long off times, there is the danger of the combustion by products being condensed in the chimney or stack. The supply rate from a public gas system furthermore has an upper limit and, generally speaking, in this case as well, smooth loading of the system without any sudden increases at peak loading times is desired. Furthermore, when the oil or gas heating is turned off, there will be great heat losses because of the convection through the chimney, which may not be stopped. Electric heating of absorption heat pumps produces the same shortcomings with respect to loading of the public line as driving of a compressor heat pump by an electric motor.
In the U.S. Pat. No. 4,070,870 (Bahel et al.) a suggestion has been made for producing hot water with the energy of the sun and storing it in a supply vessel for use, if heat is needed, simply for heating purposes or, if cooling is needed, using it for heating (after further heating in the condenser of a compressor heat pump) the generation unit of an absorption refrigeration machine. The heat energy, stored in the hot water, can not, as such, be used for operation of the absorption refrigeration machine, however, because of its low temperature level.
In the U.S. Pat. No. 4,034,569 (in part the same as the German Offenlegungsschrift specification No. 2,720,561 (Tschernev)), an account is given of a cooling system, working on the same lines as an absorption refrigeration or cooling machine, with, for example, a zeolite-water working medium system, and with heating with energy from the sun. Because, on producing a cooling effect, the generation unit is heated by solar energy, the working medium, evaporated on producing a cooling effect, has to be stored till absorption takes place again. For that reason, it is only the working medium and not the input or useful energy which is stored. U.S. Pat. Nos. 4,138,861 (Wurm) and 4,169,362 (Weil et al) disclose solid adsorption air conditioning apparatus using, inter alia, the system zeolite-water as an adsorbent-working fluid system. It is, however, not to be seen from these publications that zeolite has properties making it useful as an absorption material for an absorption heat pump system in which not only useful heat at a relatively high temperature level is produced, but, in addition to the heating effects, cooling effect (cold) is obtainable and, further operation-energy for a subsequent heat pump may be stored with good effect.
The German Pat. No. 596,308 (Normelli) describes a discontinuously working absorption refrigeration or cooling machine, in which the working medium is generated, is condensed and stored, when cheap energy, as for example overnight electricity, is on hand, at a later point in time, when a cooling effect is desired, the stored working medium is evaporated, for producing such a cooling effect, and absorbed again. The heats of condensation and absorption are to be used as well. However, wide-scale use of this system has so far not been possible because the right sort of absorption medium/working medium systems have not so far been designed, and it is, furthermore, not to be seen from the above patents that zeolite would be useful for a system, working with completely different operation properties of the type disclosed below.
Lastly, multi-stage absorption heat pumps have been suggested in German Pat. Nos. 620,249; 671,791 and 678,942, the first stage heat pump being utilized as a heat store. The operation heat or driving heat supplied to the first stage has so far been limited to temperatures below about 180.degree. C., because practical working medium systems for higher temperatures were not available. Further these multi-stage systems do not make optimum use of the heat output of the first stage.